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11.40: Nervous System

Difficulty Level: At Grade Created by: CK-12
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What body system helps you learn?

As these girls are studying, many processes are taking place. Their eyes have to take in the words on the page, and their brains have to process the meaning of the words. The brain also has to assimilate the knowledge so it can be retrieved at a later time. All these processes are controlled by the nervous system.

Introduction to the Nervous System

Michelle was riding her scooter when she hit a hole in the street and started to lose control. She thought she would fall, but, in the blink of an eye, she shifted her weight and kept her balance. Her heart was pounding, but at least she didn’t get hurt. How was she able to react so quickly? Michelle can thank her nervous system for that (Figure below).

Staying balanced on a scooter requires control of the body's muscles and awareness of the surroundings

Staying balanced when riding a scooter requires control over the body’s muscles. The nervous system controls the muscles and maintains balance.

The nervous system, together with the endocrine system, controls all the other organ systems. The nervous system sends one type of signal around the body, and the endocrine system sends another type of signal around the body. The endocrine system makes and releases chemical messenger molecules, or hormones, which tell other body parts that a change or a reaction is necessary. So what type of signal does the nervous system send?

Controlling muscles and maintaining balance are just two of the roles of the nervous system. The nervous system also lets you:

  • Sense your surroundings with your eyes and other sense organs.
  • Sense the environment inside of your body, including temperature.
  • Control your internal body systems and keep them in balance.
  • Prepare your body to fight or flee in an emergency.
  • Use language, think, learn, and remember.

The nervous system works by sending and receiving electrical signals. The main organs of the nervous system are the brain and the spinal cord. The signals are carried by nerves in the body, similar to the wires that carry electricity all over a house. The signals travel from all over the body to the spinal cord and up to the brain, as well as moving in the other direction. For example, when Michelle started to fall off her scooter, her nervous system sensed that she was losing her balance. It responded by sending messages from her brain to muscles in her body. Some muscles tightened while others relaxed. Maybe these actions moved her hips or her arms. The nervous system, working together with the muscular and skeletal systems, allowed Michelle to react to the situation. As a result, Michelle’s body became balanced again. The messages released by the nervous system traveled through nerves. Just like the electricity that travels through wires, nerve quickly carry the electrical messages around the body.

Think about how quickly all this happens. It has to be really fast, otherwise Michelle would not have been able to react. What would happen if a car pulled out unexpectedly in front of Michelle? A signal would have to go from her eyes to her brain and then to her muscles. What allows the nervous system to react so fast. It starts with the special cell of the nervous system, the neuron.


  • The nervous system sends electrical messages throughout the body and controls all other body systems.
  • The nervous system allows you to think, learn, sense your surroundings, and control your internal body systems.

Explore More

Use the resource below to answer the questions that follow.

  1. What are the major organs of the nervous system?
  2. What does the somatic nervous system do? Why is a system like this useful to organisms?
  3. What does the autonomic nervous system do? How does it differ from the somatic nervous system?


  1. What are three functions of the nervous system?
  2. What type of signals does the nervous system send? What carries these signals?
  3. What are the main organs of the nervous system?


endocrine system

endocrine system

System of glands that secrete hormones into the bloodstream.


Bundle of nerve cells.
nervous system

nervous system

Body system that sends electrical messages throughout the body; controls all other body systems.
organ system

organ system

Groups of organs that work together to perform a specific task.

Image Attributions


Difficulty Level:

At Grade


7 , 8

Date Created:

Nov 29, 2012

Last Modified:

Jan 30, 2016
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